Phase-change wallboard and mechanical night ventilation in commercial buildings: potential for HVAC system downsizing.

As thermal storage media, phase-change materials (PCMs) such as paraffin1 eutectic salts; etc. offer an order-of-magnitude increase in thermal storage capacity, and their discharge is almost isothermal. By embedding PCMs in gypsum board, plaster, or other wall -covering materials, the building structure acquires latent storage properties. Structural elements containing PCMs can store large amounts of energy while maintaining the indoor temperature within a relatively narrow range. As heat storage takes place inside the building where the loads occur, rather than at a central exterior location, the internal loads are removed without the need for additional transport energy. Distributed latent storage can thus be used to reduce the peak power demand of a building, downsize the cooling system, and/or switch to low-energy cooling sources. We used RADCOOL, a thermal building simulation program based on the finite difference approach, to numerically evaluate the thermal performance of PCM wallboard in an office building environment. We found that the use of PCM wallboard coupled with mechanical night ventilation in office buildings offers the opportunity for system downsizing in climates where the outside air temperature drops below 18 °C at night. In climates where the outside air temperature remains above 18 °C at night, the use of PCM wallboard should be coupled with discharge mechanisms other than mechanical night ventilation with outside air.